The Effects of Improved Nutrition in Early Childhood : The institute of Nutrition of Central America and Panama (INCAP) Follow-up Study; Proceedings of an IDECG workshop, July 1990, Bellagio, Italy, Supplement of The Journal of Nutrition (International Dietary Energy Consultative Group - IDECG, 1990, 113 pages)

History and design of the INCAP longitudinal study (1969-77) and its follow-up (1988-89)(¹,²)

(introductory text...)

The INCAP longitudinal study (1969-77)

The INCAP follow-up study (1988-89)

Literature cited

The INCAP follow-up study (1988-89)

Objectives and design. The INCAP follow-up study of 1988-89 was a
cross-sectional evaluation of former participants of the INCAP longitudinal
study of 1969-77. At the time of the measurement, former participants of the
longitudinal study ranged in age from 11 to 27 y. Also included in the follow-up
study were subjects of the same age living in three nearby communities that
INCAP had identified as potential study sites in the 1960s but which were not
chosen in the end (referred to as "comparison" villages).

The main hypothesis of the follow-up study was as follows:
Nutritional improvements in the critical period of gestation and the first;
three years of life ultimately produce adolescents with a greater potential for
leading healthy, productive lives. An equivalent, but briefer statement of
the central hypothesis is that "improved nutrition in early childhood
leads to enhanced human capital formation".

The richness of the longitudinal study data set allows for several
ways of operationalizing improved nutrition in early childhood. Foremost, this
can be done relative to the nutrition intervention by classifying subjects as
belonging to Atole, Fresco or comparison villages. Also, information about daily
attendance and intake of supplement permit estimates to be made of energy and
nutrient intakes from supplement over any time period for all individuals.
Finally, the study permits many other alternative definitions of childhood
nutritional status which are not based on the nutrition intervention but that
rely instead on the longitudinal information. available for children. Although
not anchored in an experimental design, measures such as growth rate s or degree
of stunting, by virtue of being responsive to the full range of factors which
influence child health (i.e. diet, infection and their determinants), provide a
wider range in nutritional status than measures of supplement. An advantage of
anthropometric measures is that they are widely used as indicators of
nutritional status and hence are familiar to the international nutrition
community.

The central hypothesis of the follow-up study refers to
"greater potential for leading healthy, productive lives" in
recognition of the fact that productivity, particularly in an economic
sense, was not measured as well as potential. Greater potential
was operationalized as improved status in terms of measures of physical growth
and body composition, maturation, work capacity, information processing,
intelligence, functional competence (reading, numeracy, general knowledge) and
educational achievement (Rivera et al.1992). Some productivity data were
collected; labor participation and earnings were obtained for all subjects for
the previous year. Nonetheless, many of the follow-up study subjects,
particularly those exposed to supplement during pregnancy and the first three
years of life, were too young in 1988-89 to allow for a meaningful exploration
of the links between early nutrition and productivity. These aspects can be more
adequately studied as the subjects become older and settled into an occupation.

A range of impact was predicted depending upon age at exposure to
the nutrition intervention. Maximum effects at follow-up were predicted for
subjects born from 1969-1974 (Table 3). These subjects were exposed to
supplement during "critical phases" of growth and development,
namely pregnancy and the first 3 y of life. The basis for this claim was the
greater degree of growth retardation observed at these ages and the lack of
demonstrated effect of the supplement on physical growth rates after 3 y of age
(Martorell and Klein 1980; Schroeder et al. 1995).

The investigators argued to NIH, the agency that funded the
research, that the follow-up study was unique because it was the first
long-term, comprehensive follow-up of a nutrition intervention. Specifically,
the follow-up study was expected to address whether the benefits of nutrition
interventions on growth and development in early childhood persist into
adolescence and beyond, to inform about effects and functions that can only be
measured later in life and to contribute to understanding the importance of
early growth and development for future status. Also, the investigators argued
that the policy implications were clear and compelling. The following statement
was included in the abstract to the first proposal submitted to NIH:

If valid, it will demonstrate that there are strong
linkages among malnutrition, human capital formation and poverty which justify
investments in health and nutrition as components of economic development
strategies.

In designing the study, the investigators were troubled by two
questions: should the study be longitudinal or cross-sectional and should the
study be carried out sometime in the future when subjects reach maturity or
should the study take place as soon as possible? The limitations of a
cross-sectional evaluation were recognized readily. It is well known that the
dynamic process of growth and maturation during adolescence can not be
adequately studied through a cross-sectional design. Also, important areas such
as fertility, employment history and wage earnings are difficult to collect
accurately from single interviews. Although a longitudinal design would have
provided better data for many outcomes, it would have increased dramatically the
complexity and the cost of the study. Cost estimates, even for a cross-sectional
survey, were already very high. For these reasons, a cross-sectional approach
was selected.

The next question had to do with the timing of the study, when to
do it? The study could proceed immediately while the subjects were adolescents
or young adults or it could be postponed till most subjects were adults. The
advantages of studying adults were recognized. One would be the elimination of
the need to control for maturity in the analyses. By virtue of studying adults,
information about truly long-term outcomes would be collected and the assessment
of effects on fertility, occupation and earnings would be more definitive.
Nonetheless, it was decided to proceed as soon as possible even though many
subjects were still adolescents, partly to learn about effects on maturity and
adolescence but more importantly, because the opportunity to carry out the study
existed and it was feared that suitable conditions may not present themselves
later. At this time, there was a team of interested researchers in place,
enthusiasm was high and funding prospects looked reasonable.

The follow-up study, as noted, included data collection in three
comparison villages chosen from six villages considered but not selected for in
the longitudinal study in 1969. These villages were of interest because they
were presumably similar to the Atole and Fresco and offered the theoretical
possibility of shedding light on what might have occurred in the study villages
in the absence of INCAP. However, it was not clear why they were not ultimately
selected for the longitudinal study. Clearly, they were not felt to be the ideal
choices. Still, the decision was made to include three of the previously
unselected communities in the follow-up study. To reduce costs and travel time,
three of the villages that were closest in distance to the four longitudinal
study villages were included for study (i.e., Subinal, Las Ovejas and El
Caulote).

Another issue that was carefully considered was that of migration.
It was feared that to leave migrants out of the study would leave open the
possibility of selection bias. On the other hand, the inclusion of migrants
would complicate the logistics of data collection and increase costs. A
compromise was reached. Migrants were included but only those who migrated to
Guatemala City, Sanarate and El Jicaro (the last two being the provincial towns
nearest to the study villages). Tracking down migrants to more dispersed areas,
it was felt, would have been too costly.

Subjects studied Census data were collected between
October 1 and December 1, 1987 and included general information about the family
(e.g., religion, number of family members, characteristics of the dwelling) and
about each family member (e.g., birth date, place of birth, migration history,
education and occupation). Follow-up data collection took place between May 1988
and June 1989; the census was continuously updated throughout this period. The
principal targets of the follow-up study were adolescents and young adults but
other groups were studied as well as noted below.

Adolescents and young adults (follow-up cohorts). These
subjects were born between January 1962 and February 1977. Records for 2393
children meeting these criteria were generated from a computer master file
prepared jointly by Cornell University and INCAP in 1983. Of the 2393 children
included in the master file 224 (9.4%) had died when the follow-up study began,
for the most part in early childhood. The 2169 subjects alive in 1988 were the
target sample in the supplemented villages, a number greater than that given in
Table 3 (i.e., 1992) because it includes subjects with no anthropometric
measures available from the longitudinal study. The target sample in the three
comparison villages (929 individuals) were subjects who had lived in these
villages between January 1969 and February 1977, according to information
obtained in the 1987 census. The total target sample therefore, including
subjects from supplemented and comparison villages, consisted of 3098 subjects.
For simplicity, these subjects are referred to hereafter as the "follow-up
cohorts". The functional domains measured in the entire follow-up cohorts
included physical growth and body composition, maturation, strength, physical
health and retrospective life history.

Special sample for the behavioral component. Measures of
information processing, intelligence, functional competence and educational
achievement were collected on all subjects born in 1966 and later. A large
number of outcome variables in the behavioral area were of interest; therefore,
the time demands for testing each subject were high. To reduce costs and the
duration of the study, the cohorts born between 1962 and 1965 were excluded.
These cohorts had received supplementation at noncritical developmental periods
(ages 4-7) and thus, minimal effects were expected. Their exclusion was
unfortunate because they would have been a useful contrast group to that
selected.

Special work capacity sample. This is a sample of ~25% of
the follow-up cohorts, excluding migrants, (539 subjects) for whom measurements
of work capacity, bioelectrical impedance, bone density and physical activity
were obtained. Based on the 1987 census, a stratified random sample of 25% of
the follow-up cohorts was selected. Details about the selection of these
subjects are provided by Haas et al. (1995).

Parents of follow-up cohorts. Anthropometric measurements
of resident parents of the follow-up cohorts were obtained to better interpret
growth patterns in the follow-up study cohorts.

A retrospective life history was conducted through interviews of
mothers, including those who had migrated to Guatemala City and to the two
provincial cities closest to the study villages (Sanarate and El Jicarol.) This
information was required to complete the reproductive histories of women for the
entire reproductive period and to obtain information about events that took
place in the families of the follow-up cohorts between 1977 and 1988, and. that
could have influenced the outcomes of interest: at adolescence. All parents were
included in the study, irrespective of whether their follow-up cohort child (or
children) still lived with them or had formed. an independent family.

Wives of the follow-up cohorts. All wives of the follow-up
cohort males, whether or not they were former participants of the INCAP
longitudinal study, were interviewed for the collection of retrospective life
history information.

Heads of households. All heads of households in which at
least one of the spouses or dependents was a follow-up cohort subject were
interviewed to obtain information on income and wealth of the family. The sample
of households included the newly formed households as well as the parents'
households.

Children <5 y of age. Anthropometric measurements were
obtained on all children <5 y of age in the seven villages to assess their
nutritional status. These data were seen as useful for estimating the degree of
secular change in the study villages through comparisons of the results with
those collected earlier in children in the longitudinal study.

Tests, exams, measurements and interviews. The
tests, exams, measurements and interviews made on the different groups are
described briefly below. For a more detailed description of the methods and a
presentation of the data forms used see Rivera (1989) and Castro and Rivera
(1992).

Follow-up cohorts. The following measurements and
examinations were made in the follow-up cohorts:

2) A clinical examination by a physician, including a medical
history, a detailed physical examination, the measurement of blood pressure,
heart and respiratory rates, body temperature and the assessment of age at
menarche (status quo and history). In addition, a vision test was performed and
examination for signs of vitamin A deficiency and goiter were made.
Abnormalities and diagnoses of diseases were recorded and treatment was provided
when needed.

3) A blood sample was collected, that was further used to
determine anemia lie and iron status.

4) A hand-wrist X-ray was obtained in males and in nonpregnant
females 18 y and younger. The X-rays were later used to assess skeletal age by
the Tanner and Whitehouse-2 method of rating. A gravindex test on urine was
performed in females 18 y and younger who had reached menarche to identify early
pregnancies. Pregnant women were not exposed to X-rays.

5) Hand strength was measured for right and left hands using a
dynamometer.

6) Follow-up cohorts were interviewed for the collection of
retrospective life history information. Spouses of follow-up subjects also were
interviewed. The female retrospective life history included information about
current reproductive status, parity and gravidity; a detailed reproductive
history (for every pregnancy: pregnancy outcome, newborn birth date, mortality,
feeding mode at time of death, prenatal care and delivery care); breast feeding
and weaning practices for any child in the last 5 y, contraceptive use,
marital/union status and history; education, occupation and migration history;
and the characteristics of the dwelling where the women had lived. The male life
history included income, occupation, education and migration history as well as
some information about accumulated wealth. In addition it contained information
about marital/union status, dependents and their ages and sexes.

7) School performance. Information from school records was
recorded including: age at first enrollment, grades attended, attendance rate
and test scores.

Sample for the behavioral component. Full details about the
behavioral data collected are given by Pollitt et al (1993). The following tests
were included:

1) Information processing. This test was applied using
a microcomputer. Computer programs were designed specifically for the purposes
of this study. Test of simple and choice reaction time, a short memory task, and
a paired associates test comprised the computerized battery.

2) Tests of functional performance. The battery included tests of
literacy, numeracy and general knowledge, which were developed locally, and two
standardized educational achievement tests of reading and vocabulary. The
achievement tests were part of the Interamerican Series used extensively in
Guatemala by faculty from the Universidad del Valle.

Work capacity sample. Physical work capacity was determined
as the oxygen consumption at maximum physical e xertion (VO2max) on a
motorized treadmill.

Besides the work capacity test, measurements of bioelectrical
impedance and bone density, using photon absorptiometry, were made in the work
capacity sample. In addition, physical activity was investigated through a
questionnaire.

2) A retrospective life history was completed, identical to the
one obtained by interview in follow-up subjects.

3) Heads of households. A detailed questionnaire regarding the
family's income during the previous year, as well as accumulated wealth over the
years was applied to heads of households. Information obtained included land
tenure, crops produced, agricultural inputs (including labor, production and
operation costs), time spent in agricultural jobs by crop produced and family
member, production, revenue and income from agriculture and other sources and
inventory of livestock ownership.

Organization and logistics of data
collection. Six working teams conducted the tests, exams,
measurements and interviews: two focused on the follow-up cohorts, one on
parents of the follow-up cohorts, one on children's anthropometry, one on work
capacity and one on migrants. Details about the composition of these teams and
about coordination and supervision of their work are given in Rivera, Martorell
and Castro (1992).

Logistics of data collection. Rotation of
teams. The data collection teams were rotated among villages. Also, data
collection in each village was staggered over the study to include both rainy
and dry seasons.

Program of appointments for follow-up cohorts. The order in
which subjects were measured was random. Subjects were scheduled to complete all
tests, measurements and interviews in three visits but most subjects chose to
complete them in 2 d and in some cases, in 1 d.

Informed consent was followed. When possible, the behavioral tests
were done before the medical examination, which involved blood collection,
because this procedure caused anxiety in some subjects. When possible, the
behavioral tests were spread across visits to avoid fatigue.

Average durations of testing were as follows: Anthropometric
measurements, hand-wrist X-rays and hand strength tests (25 min), medical
examination and collection of urine and blood samples (25 min), functional
competence and intelligence tests (160 min) and life history interview (20 min).
In general, subjects tolerated the time involvement in the study better than
expected.

Some subjects (3.6% of participants) refused to visit the testing
center but were willing to be measured at home where all but X-rays and
information processing tests could be completed. In contrast, most of the income
and wealth interviews of heads of households and a large number of life history
interviews of mothers and anthropometric measurements of parents of follow-up
cohorts were made at home, because these subjects had less time to attend the
centers.

The teams worked ~8 h/d but schedules were flexible to accommodate
the preferred hours of participation of the subjects in each village and season.
In all the villages, the teams had to work some weekends to allow for
participation of subjects who worked in the fields during weekdays until late in
the afternoon, subjects who worked out of the villages and returned during the
weekends and migrants who visited their families during the weekends.

Training, supervision and data flow. Training.
Training took ~2 mo and rigorous standardization exercises were held in all
areas. Technical errors of measurement in anthropometry were equal or better
than those reported in the literature (Pareja et al. 1989). For life history and
income and wealth questionnaires as well as for functional performance tests,
the percent agreement among interviewers usually exceeded 95%. Detailed results
of the standardization procedures are given elsewhere (Rivera 1989; Castro and
Rivera 1992).

Supervision and quality control. Supervision was
continuous. All supervisors spent ³ 2 or 3 d/wk in the field, providing
direct supervision to field workers and examining and correcting data collection
forms.

Ranges of permissible values in anthropometry were used to detect
outliers; then, either obvious errors were corrected or subjects were
reexamined. Errors in the behavioral area, the life history and the income and
wealth interviews were detected through the review of data forms. In the work
capacity area, the supervisors participated directly in data collection. After
each test, the team reviewed the results and in this manner detected and
corrected obvious errors.

Repeated measurements were made in ~10% of cases in anthropometry
and in ~4% of cases in other areas. Analyses of these data are reported in the
methods sections of papers in this volume.

Data flow, entry, verification and cleaning. Data were key
punched twice at the INCAP computer center. The data then were cleaned using
valid ranges of values and consistency checks across variables to detect errors
and outliers. Values suspected to be incorrect were sent back to the field where
the supervisor of each area corrected coding errors. For anthropometry and the
life history questionnaires, subjects were reexamined whenever errors other than
coding were found.

Primary health care activities. Efforts to
strengthen the primary health care in each of the villages were implemented in
coordination with the Ministry of Health.

A physician, hired by INCAP, instructed the nurses in several
areas, especially the government's child survival program. He visited each
village once a week to examine cases referred to him by the nurses as well as to
attend to anyone in the village wishing to see him. Drugs and medicines were
donated to the clinics to make up for the unpredictability of government
supplies. In the two villages lacking clinics, INCAP established clinics in
buildings donated by the community and hired nurses to staff them. At the end of
the study, all medical equipment in the new clinics was donated to the
communities.

Minimal dental services were provided through an arrangement with
the University of San Carlos' dental school.

Coverage rate. Coverage is defined as the rate
"participants/target sample." Participants being subjects for whom
data were available for at least one study area (Tables 5-7).

Table 5 shows rates of coverage by village and type of
village. Overall coverage was 7l. 7% with rates being slightly greater for
supplemented villages (72.6%) than for comparison villages (69.5%). Coverage
rates did not differ significantly between Atole and Fresco villages.

Table 6 presents coverage rates by migration status.
Coverage rates differed between supplemented and comparison villages; among
nonmigrant subjects, coverage rates were ~10% greater in supplemented (88.6%)
than in comparison villages (78.0%.). This is probably the result of the good
rapport built by INCAP during the 9 y of the longitudinal study. On the other
hand, coverage for migrants was slightly less in supplemented (40.7%) than
comparison villages (44.7%). This may be due to differences in how the target
sample was defined in supplemented and comparison villages. The target sample of
migrants in the comparison villages was identified using information available
in the 1987 census. Therefore, only adolescent migrants whose families were
still living in the villages at the time of the follow-up census were selected.
In contrast, in the supplemented villages, follow-up cohorts whose entire
families had migrated before the beginning of the follow-up study also were
selected, using records from the longitudinal study. Some of these migrant
families were located using information provided by neighbors and relatives;
however, as a result of the absence of parents or close relatives, follow-up
cohorts belonging to these families were much more difficult to locate than
migrants whose families were still living in the villages.

Coverage rates for migrants were overall much lower than those for
nonmigrants because of the difficulty of locating migrants and because data
collection in migrants was restricted to those living in Guatemala City and two
provincial cities. The decision to focus on these locations was based on
resource restrictions and the fact that information available at the beginning
of the study indicated that ~64% of the subjects for whom locations were known
lived in one of these three cities. Coverage for migrants known to have moved to
these three cities was 62%. For the entire migrant sample, coverage was 42%
(Table 6).

Coverage rates for females were greater in both migrants and
nonmigrants. In migrants, coverage rates were 45.6% and 36.9% for females and
males respectively; these patterns were similar in supplemented (females:
176/394 = 44.75% and males: 120/333 = 36.0%) and comparison villages (females:
65/134 = 48.5% and males: 40/101 = 39.6%). In nonmigrants, coverage for females
was 89.7% and for males 81.2%. Coverage rates were greater in females in
supplemented villages (females: 623/666 = 93.5% and males: 655/776 = 84.4%) as
well as in comparison villages (females:278/339=82.0% and males:263/255=74.1%).

TABLE 7 Percent coverage in the follow-up exhorts by
birth cohorts and gender

Subjects were classified into four birth cohorts according to ages
of exposure to supplementation (Table 3). Table 7 presents coverage rates
by cohort and village. In general, Cohort I has the highest coverage rates,
followed by Cohort II and finally by Cohorts III and IV. Younger subjects may
have had more time to participate in the various tests and interviews than older
subjects.

Table 8 presents coverage rates for the different study
domains by village type. Coverage rates were ~ 70% for most domains. The low
coverage for blood collection deserves comment. Interviews of subjects who had
refused to participate and of their families revealed that anxiety related to
blood collection was one of the principal reasons for nonparticipation. Some
subjects felt that the very small amount of blood collected (5 mL) was very
large relative to the total blood volume in an adult. In one village, there were
rumors that the blood was being sold. To remedy the situation, subjects were
informed that blood collection was not essential for participation in the rest
of the tests, measurements and interviews. In addition, subjects were reminded
that blood samples also were used for the diagnosis of anemia, with treatment
provided when necessary. Subsequently the refusal rate declined, though refusals
to provide a blood sample among participants in the study remained high.

Table 8 also presents coverage rates for the different study
domains in the comparison villages. Coverage rates were slightly less than found
in the supplemented villages, but follow the same patterns. For the work
capacity test, more subjects than originally planned were examined in comparison
villages (see Haas et al. 1995).

Coverage rates for anthropometric measurements of parents of the
follow-up sample was 82.4%, with no difference between supplemented (809/979 =
82.6%) and comparison villages (386/472 = 81.8%). Similar coverage rates were
obtained for the life history of mothers of the follow-up samples (82.7%), with
similar coverage rates for supplemented (452/543 = 83.2%) and comparison
villages (207/253 = 81.8%). In contrast, coverage of the income and wealth
questionnaire applied to heads of households was lower (62.0%), with rates being
similar in supplemented (62.5%) and comparison villages (60.7%). The low
coverage rates for the income and wealth interviews were due in part to the long
time required to obtain the information and the fact that most of the heads of
households worked in agriculture and were away during most of the day.

TABLE 8 Coverage rates by study domain and village
type for the follow-up cohorts

Full details about design and methods, such as contained in this
article, are often not readily available in the literature. The INCAP
longitudinal and follow-up studies are among the most important sources of
information from developing countries about child growth, development and
nutrition and it is likely that there will be continued analyses of these data
for years to come. It is important to have a faithful record of the design,
objectives, methods and procedures, particularly for the benefit of analysts who
may not have been directly involved with the
studies.